1. Field of the Invention
The field of this invention lies within the dot matrix printing art. More particularly, it lies within the field of dot matrix printing that is accomplished by what is known as a line printer. Such line printers are known to have a hammerbank with a multiplicity of hammers thereon which are released from permanent magnetic retention by an electrical coil to allow release thereof. In particular, this invention relates to the hammerbank itself and the respective cover for the print hammers.
2. Prior Art
The prior art with regard to line printers has evolved over the years. Such line printers are known to have a plurality of hammers on a hammerbank. These hammers are provided with tips which strike a ribbon in order to impact a print media thereunder. Upon striking the print media with the tips against the print ribbon, an impacted dot is printed to provide dot matrix printing.
It is known that these hammers can be retained by a permanent magnet in a sprung position. When the permanent magnetism is released by coils overcoming the permanent magnetism, the hammers are then released in order to impact the print ribbon against the print media to create the dot matrix printing known in the art.
The operation of such hammerbanks is generally fraught with multiple dynamic loadings. These multiple dynamic loadings are the product of numerous reciprocations of the hammerbank, release of the hammers and vibrations.
The foregoing, creates dynamic force moments and torque on the hammerbank which can oftentimes distort the placement of the dots of the dot matrix printer against the media that is to be printed upon. In such cases, the net result is that a significant problem is associated with such printing due to the inconsistencies and displacement of the printed dots with respect to each other.
It has been felt that if the dynamic motion which distorts a hammerbank, even if it is distorted ever so slightly, can be diminished or somewhat eliminated, that improved printing can be accomplished. In order to do this, the respective hammerbank and cover relationships should be moderated to improve the stiffness so as to reduce the dynamic distortion of the hammerbank and cover assembly during the reciprocation and firing of the hammers.
The prior art hammerbanks generally incorporated a simple flat cover stamped from magnetic stainless steel which magnetically interacted with the hammerbank and the hammersprings. This flat cover was located with respect to the hammerbank and the hammerspring tips by incorporation of two punched holes. One of the holes was round and the other oblong, which were placed over two steel locating pins on the hammerbank. The acceleration forces of the hammerbank would eventually wear the round alignment holes larger. These alignment holes were placed so that the tips were initially in the center of the protrusion holes. In order to improve this, positive clamping of the cover to the hammerbank by screws helped to prevent the cover moving with respect to the tips.
The hammerbank covers of the prior art were retained by multiple slots containing attracting magnetic components along the elongated portions thereof. This relationship created a deflectable and yielding hammerbank cover during printing because of dynamic and static forces. One of the end results was that this yielding increased tip protrusion of the hammerbank tips which can cause ribbon snagging. In order to improve this, positive support of the cover of this invention next to the tip locations via a pedestal touching the hammerbank creates very high stiffness eliminating or greatly reducing deflection of the hammerbank.
Additionally thereto, the print mask had to be bonded or welded to the magnetic stainless steel cover thereby creating a problem associated with replacement parts, wear, repair, and overall manufacturing procedures. In order to improve this, easy replacement is created by bolting the mask to the cover.
The new cover of this invention creates a hammerbank cover which is non-magnetic and is machined from an aluminum extrusion. The hammerbank cover is bolted to the frame with the mask bolted to the cover. This increases the overall stiffness of the hammerbank, cover, and mask combination. The net result is to provide for improved flatness, and reduction of dynamic deflections that change the relationship of the hammerbank with regard to its normal position and geometry.
The invention provides an improved hammerbank cover that is subject to less deformation, deflection, and provides for a lesser incidence of wear and increased serviceability.
The foregoing stiffness helps to diminish vibration and results in improved printing characteristics.
The cover has a pedestal machined next to the ends of the hammersprings. The pedestal rests upon the hammerbank precision machined surfaces. This provides a more accurate tip protrusion manufacturing technique without adjustment.
The alignment of the holes of the cover with respect to the hammerbank and hammerspring location is fixed and does not change significantly. To the contrary, the former stainless steel covers shifted and the alignment holes were somewhat shifted during turnaround of the hammerbank or the attendant reciprocation.
The increased stiffness of the hammerbank and cover combination provides for improved flatness and less deflection and is enhanced by the pedestal geometry. Further to this extent, during repairs, replacement, or changes, the mask can be bolted to the cover and easily changed for improved replacement, and associated and related operational procedures.